Process for producing brominated butyl rubber

ABSTRACT

The invention relates to an energy efficient, environmentally favourable process for the preparation of brominated butyl rubbers, that uses a bromination agent and a oxidizing agent in order to enhance the utilization of bromine contained in the bromination agent. In a preferred embodiment a common medium for both solution polymerization and subsequent bromination of the rubber is employed.

FIELD OF THE INVENTION

The invention relates to an energy efficient, environmentally favourableprocess for the preparation of brominated butyl rubbers, that usesbromine or a bromine precursor or both and a oxidizing agent in order toenhance the utilization of bromine. In a preferred embodiment a commonaliphatic medium for both solution polymerization and subsequentbromination of the rubber is employed.

BACKGROUND

Butyl rubbers such as isobutene-isoprene rubber (also denoted as IIR)and their halogenated analogues are an important class of syntheticrubbers.

In the conventional process for producing brominated butyl rubber (alsodenoted as bromobutyl rubber or BIIR) e.g. isobutene and isoprene arefirst polymerized in a polar halohydrocarbon medium, such as methylchloride with an aluminum based initiating system, typically eitheraluminum trichloride (AlCl₃) or ethyl aluminum dichloride (EtAlCl₂). Thebutyl rubber does not appreciably dissolve in this polar medium, but ispresent as suspended particles and so this process is normally referredto as a slurry process. Residual monomers and polymerization medium arethen steam stripped from the butyl rubber, before it is dissolved in abromination medium, typically a non-polar medium such as hexane. Thebromination process ultimately produces the final brominated product.The conventional process therefore employs separate polymerization andbromination steps employing two different media. The use of a polarmedium for polymerization and a non-polar medium for brominationnecessitates intermediate stripping and dissolving steps and isinefficient from an energy point of view.

The step of separating the monomers and methyl chloride from the butylrubber is conducted before bromination in order to avoid the formationof highly toxic byproducts from the reaction of bromine with residualmonomers. The normal boiling points of the components used in theprocess are: methyl chloride, −24° C.; isobutylene, −7° C.; andisoprene, 34° C. Any stripping process that removes the heavier of theresidual monomers (isoprene) will also remove essentially all of themethyl chloride and isobutylene. The process of removing all of theun-reacted components from the rubber slurry requires significantamounts of energy. The greater molecular weight (and therefore higherboiling point) of the brominated monomers also precludes the removal ofthese species following the bromination process.

Solution processes for the polymerization of butyl rubber have beenknown for many years and are described for example in CA 1,019,095 andU.S. Pat. No. 3,361,725, where iso-pentane and n-hexane are used aspolymerization medium and WO 2010/006983, which discloses the use of analiphatic medium comprising at least 50 wt.-% of one or more aliphatichydrocarbons having a boiling point in the range of 45° C. to 80° C. ata pressure of 1013 hPa as the preferred polymerization medium.

WO 2010/006983 further discloses a subsequent standard halogenationprocess where bromine is used as bromination agent. A major inefficiencyof this process is that the theoretical fraction of bromine present inthe reaction mixture which can be introduced into the polymer is atmaximum 50% of the theory, and the actual utilization observed incommercial plants is usually less than 45%. Most of the remainingbromine is lost due to formation of hydrogen bromide as a by-productwhich, under normal conditions, does not brominate the polymer anyfurther. Hydrogen bromide is subsequently neutralized with a basicmaterial such as sodium hydroxide solution and washed off the bromobutylrubber, as described for example in U.S. Pat. No. 5,077,345. As aconsequence, large amounts of diluted alkali metal bromides or alkalineearth metal bromides are disposed off every year.

A known method to enhance the bromine utilization during butyl rubberbromination involves the application of at least 0.5 mol per mol ofbrominating agent of an oxidizing agent such as hydrogen peroxide oralkali or alkaline earth metal hypochlorite, optionally in the presenceof an emulsifier which reoxidizes the hydrogen bromide back to elementalbromine. The regenerated bromine is thus available for furtherbromination of butyl rubber, thereby significantly increasing thebromine utilization. Such processes are disclosed for example in U.S.Pat. No. 3,018,275, U.S. Pat. No. 5,681,901 and EP 803 517 A. Theutilization of bromine in U.S. Pat. No. 5,681,901 is at maximum 84% foremulsions comprising an oxidizing agent and at maximum 73% forexperiments without emulsifier. The solvent used for bromination wascyclohexane.

EP 709 401 A discloses a process for improving the brominationefficiency in rubber bromination processes by carrying out thebromination reaction in the presence of elemental bromine and an aqueoussolution of an organic azo compound such as azodiisobutyronitrile and/oran alkali or alkaline earth metal hypochlorite. However, there stillremains a need for an efficient, environmentally favourable process forthe preparation of bromobutyl rubbers that significantly reduces energyand raw material consumption and simultaneously allows to obtainbrominated rubbers with a desirable microstructure.

SUMMARY OF THE INVENTION

There is now provided a process for the preparation of cementscomprising aliphatic medium and at least one brominated butyl rubbercomprising at least the steps of:

-   a) providing a butyl rubber cement comprising    -   A) 5 to 30 wt-%, preferably 8 to 25 wt-%, more preferably 10 to        22 wt.-% of at least one, preferably one butyl rubber    -   B) 0 to 5 wt-%, preferably 0 to 0.9 wt-%, more preferably 0 to        0.6 wt.-% and more preferably 0 to 0.4 wt.-% of water    -   C) and an amount of an aliphatic medium comprising at least 50        wt.-% of one or more aliphatic hydrocarbons having a boiling        point in the range of 45.0° C. to 80.0° C. at a pressure of 1013        hPa, selected in such a manner that the sum of A), B) and C)        adds up to from 96 to 100 wt-%, preferably to from 98 to 100        wt.-% and more preferably from 99 to 100 wt.-% and even more        preferably 100 wt.-% of the total amount of butyl rubber cement-   b) brominating the butyl rubber or the butyl rubbers contained in    the butyl rubber cement provided in step a) with elemental bromine    in the presence of an added aqueous oxidizing agent in order to    obtain a heterophasic mixture at least comprising    -   a cement comprising aliphatic medium and brominated butyl rubber        and    -   an aqueous phase and either-   c) adjusting the pH-value of the aqueous phase, preferably within    the heterophasic mixture obtained according to step b), to 6 to 13,    preferably 8 to 12, more preferably 8 to 11 and even more preferably    9 to 10 using a base-   d1) separating the cement comprising aliphatic medium and brominated    butyl rubber from the aqueous phase    or-   d2) separating the heterophasic mixture obtained according to    step b) to obtain the cement comprising aliphatic medium and    brominated butyl rubber and an aqueous phase and-   d₃) washing the cement comprising aliphatic medium and brominated    butyl rubber with an aqueous mixture, preferably an aqueous solution    of a base.

The scope of the invention encompasses any possible combination ofdefinitions, parameters and illustrations listed herein whether ingeneral or within areas of preference.

BRIEF DESCRIPTION OF THE DRAWING

Having summarized the invention, preferred embodiments thereof will beexemplarily described with reference to FIG. 1 which shows a processflow diagram for a process according to the present invention thatfurther depicts a preferred method of preparing the rubber cementemployed in step a as well as a preferred method of isolating thebrominated butyl rubber.

DETAILED DESCRIPTION

In step a) a butyl rubber cement is provided which comprises

-   A) 5 to 30 wt-%, preferably 8 to 25 wt-%, more preferably 10 to 22    wt.-% of at least one, preferably one butyl rubber-   B) 0 to 0.9 wt-%, preferably 0 to 0.6 wt.-% and more preferably 0 to    0.4 wt.-% of water-   C) and an amount of an aliphatic medium comprising at least 50 wt.-%    of one or more aliphatic hydrocarbons having a boiling point in the    range of 45° C. to 80° C. at a pressure of 1013 hPa, selected in    such a manner that the sum of A), B) and C) adds up to from 96 to    100 wt-%, preferably to from 98 to 100 wt.-% and more preferably    from 99 to 100 wt.-% of the total amount of butyl rubber cement

The remainder to 100 wt.-%, where existent, may comprise or consist offor example additives and auxiliary products typically added to butylrubbers, such as antioxidants, foaming agents, anti-aging agents, heatstabilizers, light stabilizers, ozone stabilizers, processing aids,plasticizers, tackifiers, blowing agents, dyestuffs, pigments, waxes,extenders, organic acids, inhibitors which are well known to the rubberindustry.

The butyl rubber cement comprises at least one butyl rubber as componentA). The term “butyl rubber” as used herein denotes a co-polymercomprising repeating units derived from

-   -   at least one, preferably one C₄ to C₇ isoolefin and    -   at least one, preferably one C₄ to C₁₄ conjugated diene and    -   either no, one or more than one further co-polymerizable        monomers.

Preferred C₄ to C₇ isoolefins are isobutene, 2-methyl-1-butene,3-methyl-1-butene, 2-methyl-2-butene and mixtures thereof, wherebyisobutene is more preferred.

Preferred C₄ to C₁₄ conjugated dienes are butadiene, isoprene,2,4-dimethylbutadiene, piperyline, 3-methyl-1,3-pentadiene,2,4-hexadiene, 2-neopentylbutadiene, 2-methyl-1,5-hexadiene,2,5-dimethyl-2,4-hexadiene, 2-methyl-1,4-pentadiene,2-methyl-1,6-heptadiene, cyclopentadiene, methylcyclopentadiene,1,3-cyclohexadiene, 1-vinyl-1,3-cyclohexadiene and mixtures thereof,whereby isoprene, butadiene and cyclopentadiene are more preferred andisoprene is even more preferred.

As further co-polymerizable monomers, any monomer copolymerizable withthe isoolefins and/or conjugated dienes known by the skilled in the artcan be used. Preferred further co-polymerizable monomers includeα-methyl styrene, p-methyl styrene, α-chlorostyrene, p-chlorostyreneindene and β-pinene.

In one embodiment, the butyl rubber comprises repeating units derivedfrom 92.0 to 99.5, preferably 92.0 to 99.0 and more preferably 97.5 to98.5 or 94.0 to 96.6 mol-% of at least one, preferably one C₄ to C₇isoolefin; preferably isobutene and 0.5 to 8.0, preferably 1.0 to 8.0and more preferably 1.5 to 2.5 or 3.5 to 6.0 mol-% at least one,preferably one C₄ to C₁₄ conjugated diene, preferably isoprene.

In one further embodiment, the butyl rubber comprises repeating unitsderived from

-   i) at least one, preferably one C₄ to C₇ isoolefin; preferably    isobutene-   ii) 0.5 to 8.0, preferably 1.0 to 8.0 and more preferably 1.5 to 2.5    or 3.5 to 6.0 mol-% at least one, preferably one C₄ to C₁₄    conjugated diene, preferably isoprene and-   iii) 0.1 to 20, preferably 1 to 20 wt-% of further co-polymerizable    monomers whereby the repeating units derived from i), ii) and iii)    add up to 100 mol-% of the repeating units contained in the butyl    rubber.

Particularly preferred butyl rubbers are copolymers of isobutene andisoprene comprising 1.5 to 2.5 mol-% repeating units derived fromisoprene.

Preferably, the mass average molecular weight of butyl rubber Mw isbetween 30,000 and 2,000,000 g/mol, preferably between 50,000 and1,000,000 g/mol more preferably between 300.000 and 1,000,000 g/mol andeven more preferably from 350,000 to 600,000 g/mol, yet more preferably375,000 to 550,000 g/mol and most preferably 400,000 to 500,000 g/mol.If not mentioned otherwise, molecular weights are obtained using gelpermeation chromatography in tetrahydrofuran (THF) solution usingpolystyrene molecular weight standards.

As component C) of the cement provided in step a) of the processaccording to the invention an aliphatic medium comprising at least 50wt.-% of one or more aliphatic hydrocarbons having a boiling point inthe range of 45.0° C. to 80.0° C. at a pressure of 1013 hPa is employed.It was found that the use of a solvent having a higher content orconsisting of compounds having a boiling point of more than 80.0° C. at1013 hPa would cause difficulties in the separation from the rubberafter bromination. The solution viscosity provided by use of suchsolvents is then significantly higher making the solution more difficultto handle and to separate in step d).

In one embodiment of the invention the aliphatic medium comprises atleast 80 wt.-% of one or more aliphatic hydrocarbons having a boilingpoint in the range of 45.0° C. to 80.0° C. at a pressure of 1013 hPa,preferably at least 90 wt.-%, even more preferably at least 95 wt.-% andyet even more preferably at least 97 wt.-%. Aliphatic hydrocarbonshaving a boiling point in the range of 45.0° C. to 80.0° C. at apressure of 1013 hPa include cyclopentane, 2,2-dimethylbutane,2,3-dimethylbutane, 2-methylpentane, 3-methylpentane, n-hexane,methylcyclopentane and 2,2-dimethylpentane.

The aliphatic medium may either further comprise other compounds whichare at least substantially inert under bromination conditions or not.Such as other compounds which are at least substantially inert underbromination conditions include aliphatic hydrocarbons having a boilingpoint of more than 80.0° C. at a pressure of 1013 hPa includingcyclohexane, n-heptane and n-octane and aliphatic hydrocarbons having aboiling point of less than 45.0° C. at a pressure of 1013 hPa includingpropanes, butanes and acyclic pentanes, furthermore halohydrocarbonssuch as methyl chloride and other chlorinated aliphatic hydrocarbonswhich are at least substantially inert under bromination conditions aswell as hydrofluorocarbons whereby hydrofluorocarbons are for examplethose represented by the formula: C_(x)H_(y)F_(z) wherein x is aninteger from 1 to 20, alternatively from 1 to preferably from 1 to 3,wherein y and z are integers and at least one.

In another preferred embodiment of the invention the aliphatic medium issubstantially free of halohydrocarbons.

In another embodiment of the invention the aliphatic medium has acontent of cyclic aliphatic hydrocarbons of less than 25 wt.-%,preferably less than 20 wt.-%, more preferably of from 0.01 to 20 wt.-%,even more preferably of from 5 to 20 wt.-%.

In another embodiment of the invention the aliphatic medium has acontent of cyclohexane (boiling point: 80.9° C. at 1013 hPa) of lessthan 5 wt.-%, preferably less than 2.5 wt.-%.

As used hereinbefore and hereinafter the term “substantially free ofhalohydrocarbons” means a content of halohydrocarbons within the commonaliphatic medium of less than 2 wt.-%, preferably less than 1 wt.-%,more preferably less than 0.1 wt.-% and even more preferably absence ofhalohydrocarbons.

The butyl rubber cement employed in step a) contains from 0 to 0.9 wt-%,preferably 0 to 0.6 wt.-% and more preferably 0 to 0.4 wt.-% of water.This amount of water typically results from air humidity or traces ofwater present in the aliphatic medium but may, even though notpreferred, be added to the butyl rubber cement.

The butyl rubber cement may be prepared by dissolving butyl rubber inthe aliphatic medium, or by solvent replacement as disclosed in U.S.Pat. No. 5,021,509, which is herein incorporated by reference. In apreferred embodiment however, the butyl rubber cement employed in stepa) is prepared in process comprising at least the steps of

-   pre-a1) providing a reaction medium comprising    -   an aliphatic medium comprising at least 50 wt.-% of one or more        aliphatic hydrocarbons having a boiling point in the range of        45° C. to 80° C. at a pressure of 1013 hPa, and    -   a monomer mixture comprising at least one C₄ to C₇ isoolefin, at        least one C₄ to C₁₄ conjugated diene and either no one or more        than one further co-polymerizable monomers.    -   in a mass ratio of monomer mixture to aliphatic medium of from        35:65 to 99:1, preferably from 50:50 to 85:15 and even more        preferably from 61:39 to 80:20;-   pre-a2) polymerizing the monomer mixture within the reaction medium    to form a butyl rubber solution comprising a butyl rubber which is    at least substantially dissolved in the medium comprising the    aliphatic medium and residual monomers of the monomer mixture;-   pre-a3) separating residual monomers of the monomer mixture from the    butyl rubber solution to form the butyl rubber cement, whereby the    separation is preferably performed by distillation.

As used hereinabove the term “at least substantially dissolved” meansthat at least 70 wt.-%, preferably at least 80 wt.-%, more preferably atleast 90 wt.-% and even more preferably at least 95 wt.-% of the butylrubber polymer obtained according to step b) are dissolved in themedium.

It is within the scope of the present invention that the composition ofthe aliphatic medium may have a slightly varying composition before andafter removal of the un-reacted monomers due to different boiling pointsof its components. In an optional step pre-a4) additional aliphaticmedium of the same or different composition as employed in step pre-a1)may be added to the butyl rubber cement obtained in step pre-a3) inorder to adjust the butyl rubber concentration or the aliphatic mediumcomposition.

Since the aliphatic medium employed in step pre-a1) is used as solventin the polymerization according to step pre-a2) as well as in thesubsequent bromination of step b) the overall energy efficiency and rawmaterial utilization of the process is further improved by eliminatingthe need to separate the butyl rubber from a first diluent or solventused for polymerization, then re-dissolve it in a second solvent forbromination. This integrated process therefore provides improved energyand raw material efficiency and a reduction in the number of processsteps as compared with conventional non-integrated processes for makingbrominated butyl rubbers.

It was further found that the specific composition of the aliphaticmedium further allows to reduce the solution viscosity in thepolymerization process which is typically performed at low temperatures.

In an embodiment of the invention the polymerization according to steppre-a2) and the provision of a solution according to step pre-a1) iseffected using a solution polymerization reactor. Suitable reactors arethose known to the skilled in the art and include commonly knownflow-through polymerization reactors.

Step pre-a3) of the process may employ distillation to separateun-reacted residual monomers, i.e. the isoolefin monomers and themultiolefin monomers from the medium. This mitigates the formation ofundesirable bromination byproducts from the unreacted monomers. If stepspre-a1) to pre-a3) are used to prepare the butyl rubber cement to beemployed in step a) and distillation is employed to perform step pre-a3)the C₄ to C₇ isoolefins and C₄ to C₁₄ conjugated dienes and the optionalfurther co-polymerizable monomers employed are limited to those having aboiling point below 80.0° C. at a pressure of 1013 hPa, preferably below60.0° C. at a pressure of 1013 hPa, more preferably below 45.0° C. at apressure of 1013 hPa and even more preferably below 40.0° C. at apressure of 1013 hPa.

It is clear that the boiling point of the monomers may be higher than45.0° C. at a pressure of 1013 hPa, if the aliphatic medium comprisesaliphatic hydrocarbons having a boiling point which is higher than thatof the highest boiling component of the monomer mixture but still below80.0° C. at a pressure of 1013 hPa.

The specific ratio of monomers necessary in step pre-a1) to obtain abutyl rubber according to the specifications given in specificembodiments of step a), in particular with respect to Mw and monomerincorporation depends on several factors such as temperature andinitiator employed in step pre-a1), the exact solvent composition andviscosity just to name a few and which are well known to those skilledin the art. However, the best way to obtain a desired butyl rubber maybe easily determined by very few routine experiments.

The polymerization in step pre-a2) is initiated by at least onepolymerisation initiator, which are for example selected from the groupof cationic initiators, whereby the term cationic initiator denotes andincludes initiators capable of initiating cationic polymerizations.

Suitable cationic initiators are those producing protons, carbocationsor silylium cations capable of initiating cationic polymerizations.

Such cationic initiators include but are not limited to

-   -   reaction products of        -   at least one lewis acid such as aluminum trihalides such as            aluminium trichloride, titanium halides such as titanium            tetrachloride, stannous halides such as stannous            tetrachloride, boron halides such as boron trifluoride and            boron trichloride, antimony halides such as antimony            pentachloride or antimony pentafluoride or at least one            organometal compound such as dialkylaluminum halides such as            diethylaluminum chloride, alkylaluminum dihalides such as            ethylaluminum dichloride or a mixture of the aforementioned            lewis acids and/or organometal compounds and        -   at least one proton source such as water, alcohols such as            C₁ to C₁₂ aliphatic alcohols like methanol, ethanol or            isopropanol, phenols, carboxylic acids, sulfonic acids,            thiols or inorganic acids such as dihydrogensulfide,            hydrogen chloride, hydrogen bromide or sulphuric acid    -   carbocationic compounds of formula (I)

[CR¹R²R³]⁺An ⁻  (I)

-   -   -   wherein R¹, R² and R³ are independently hydrogen,            C₁-C₂₀-alkyl or C₅-C₂₀-aryl with the proviso that either one            or none of R¹, R² and R³ is hydrogen and        -   An⁻ denotes a monoanion or 1/p equivalent of a p-valent            anion        -   or

    -   silylium compounds of formula (II)

[SiR¹R²R³]⁺An ⁻  (II)

-   -   -   wherein R¹, R² and R³ and An⁻ have the same meaning as set            forth above for formula (I)

    -   or mixtures of the aforementioned compounds and reaction        products

The preferred molar ratio of lewis acids or organometal compounds andthe proton sources is in the range of from 1:0.0001 to 1:5, preferablyfrom 1:0.5 to 1:3 and more preferably from 1:0.5 to 1:2.

In formulae (I) and (II) R¹, R² and R³ are preferably independentlyselected from the group consisting of phenyl, tolyl, xylyl and biphenyl,methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, cyclohexyl,n-octyl, n-nonyl, n-decyl, n-dodecyl, 3-methylpentyl and3,5,5-trimethylhexyl.

In formulae (I) and (II) An⁻ preferably denote an anion of formula (III)

[M(R⁴)₄]⁻  (III)

wherein

-   M is boron, aluminum, gallium or indium in the +3 formal oxidation    state and-   R⁴ is independently, more preferably identically, selected from the    group consisting of hydride, dialkylamido, halide such as chloride,    C₁-C₂₀-alkyl or C₅-C₂₀-aryl, C₁-C₂₀-haloalkyl or C₅-C₂₀-haloaryl.

Preferred cationic initiators are

-   -   reaction products of        -   at least one lewis acid such as aluminum trihalides such as            aluminium trichloride, titanium halides such as titanium            tetrachloride, stannous halides such as stannous            tetrachloride, boron halides such as boron trifluoride and            boron trichloride, antimony halides such as antimony            pentachloride or antimony pentafluoride or at least one            organometal compound such as dialkylaluminum halides such as            diethylaluminum chloride, alkylaluminum dihalides such as            ethylaluminum dichloride or a mixture of the aforementioned            lewis acids and/or organometal compounds and        -   at least one proton source such as water, alcohols such as            C₁ to C₁₂ aliphatic alcohols such as methanol, ethanol and            isopropanol, phenols, carboxylic acids, sulfonic acids,            thiols or inorganic acids such as dihydrogensulfide,            hydrogen chloride, hydrogen bromide or sulphuric acid as            cationic initiator and

More preferred cationic initiators are reaction products ofdiethylaluminum chloride or ethylaluminum dichloride or mixtures thereofwith at least one proton source such as water, alcohols such as C₁ toC₁₂ aliphatic alcohols like methanol, ethanol and isopropanol, phenols,carboxylic acids, thiols or inorganic acids such as dihydrogensulfide,hydrogen chloride, hydrogen bromide or sulphuric acid is used, wherebywater and hydrogenchloride are even more preferred and water isparticularly preferred.

The preferred molar ratio of diethylaluminum chloride or ethylaluminumdichloride or mixtures thereof with such proton sources or preferablyhydrogen chloride and water and more preferably water is in the range offrom 1:0.01 to 1:3, more preferably from 1:0.5 to 1:2.

Particularly preferred cationic initiators are reaction products ofmixtures of diethylaluminum chloride and ethylaluminum dichloride, inparticular the 1:1 molar mixture which is also called ethylaluminumsesquichloride with hydrogen chloride or water, preferably water,whereby amount of water or hydrogen chloride to aluminium is between 50and 200 mol-%.

The polymerization initiators comprising diethylaluminum chloride andethylaluminum dichloride are typically and preferably employed as 0.5-10wt % solution in hexane in an amount of from 0.0001 to 20 wt.-%, morepreferably 0.01 to 10 wt.-% and even more preferably 0.05 to 5 wt.-% ofthe reaction medium employed in step pre-a2).

In general the polymerization initiators are preferably employed in anamount of from 0.0001 to 20 wt.-%, more preferably 0.01 to 10 wt.-% andeven more preferably 0.02 to 5 wt.-% of the reaction medium employed instep pre-a2).

In one embodiment, the process temperature of step pre-a2) is in therange of −100° C. to −40° C., preferably in the range of −95° C. to −60°C., more preferably in the range of −80° C. to −60° C.

Although higher temperatures are desirable in that energy usage forrefrigeration and pumping (due to lower viscosity at higher temperature)are reduced, this generally leads to lower molecular weight polymersthat are not as commercially desirable. However, due to the use of highmonomer to aliphatic medium ratios in the present invention, a reducedbut still acceptable molecular weight can be obtained with highertemperatures.

Therefore, in an alternative embodiment, temperatures in the range of−50° C. to lower than −75° C., preferably −55° C. to −72° C., morepreferably −59° C. to −70° C., yet more preferably −61° C. to −69° C.,are used while still obtaining the desired molecular weight of butylrubber.

The viscosity of the butyl rubber solution obtained in step pre-a2) atthe temperature employed for polymerization is preferably less than 2000cP, preferably less than 1500 cP, more preferably less than 1000 cP. Amost preferred range of viscosity is from 500 to 1000 cP. All givenviscosities refer to the extrapolated zero shear viscosity. The Zeroshear viscosity is extrapolated from measurements at given temperatureusing a Haake Rheostress RS 150 viscosimeter or a rotational rheometerof cone-plate type for very viscuous samples. The extrapolation isperformed by taking a best fitting 2^(nd) order polynomial to reflectthe shear stress vs shear rate graph obtained from the measurements. Thelinear portion of the polynomial reflects the slope at a shear rate ofzero and thus is the zero shear viscosity.

The solids content of the butyl rubber solution obtained in step pre-a2)is preferably in the range of from 3 to 25%, more preferably 10 to 20%,even more preferably from 12 to 18%, yet more preferably from 14 to 18%,even more preferably from 14.5 to 18%, still more preferably 15 to 18%,most preferably 16 to 18% by weight. As described previously, highersolids contents are preferred, but entail increased solution viscosity.The higher monomer to aliphatic medium ratios used in the presentprocess allow higher solids contents to be achieved than in the past andadvantageously also permit use of the aliphatic medium for bothpolymerization and bromination.

As used herein the term “solids content” refers to weight percent of thepolymer obtained according to step pre-a2) i.e. in polymerization andpresent in the rubber solution.

In step pre-a3), un-reacted residual monomers are removed from thesolution following polymerization. This is preferably done using adistillation process. Distillation processes to separate liquids ofdifferent boiling points are well known in the art and are described in,for example, the Encyclopedia of Chemical Technology, Kirk Othmer, 4thEdition, pp. 8-311, which is incorporated herein by reference.

The degree of separation is largely dependent upon the number of traysused in the column. An acceptable and preferred level of residualmonomers in the solution following separation is less than 20 parts permillion by weight. About 40 trays have been found sufficient to achievethis degree of separation. Separation of the aliphatic medium from themonomers is not critical and contents of for example up to 10 wt.-% ofcomponents of the aliphatic medium are acceptable in the overhead streamfrom the distillation process. In a preferred embodiment the contents ofcomponents of the aliphatic medium in the overhead stream from thedistillation process are less than 5 wt.-%, more preferably less than 2wt.-%, even more preferably less than 1 wt.-%.

In one embodiment the monomers removed in step pre-a3) are recycled intostep pre-a1), preferably after purification. Purification of monomersmay be carried out by passing them through adsorbent columns containingsuitable molecular sieves or alumina containing adsorbent materials. Inorder to minimize interference with the polymerization reaction, thetotal concentration of water and substances such as alcohols and otherorganic oxygen containing compounds that act as poisons to the reactionare preferably reduced to less than 50 parts per million, preferablyless than 10 parts per million on a weight basis. The proportion ofmonomers that are available for recycle depends on the degree ofconversion obtained during the polymerization process. For example,taking a ratio of monomer to aliphatic medium of 66:34, if the solidslevel in the rubber solution produced is 10%, then 85% of the monomersare available to be returned in the recycle stream. If the solids levelis increased to 18%, then 73% of the monomers are available for recycle.

In a preferred embodiment the polymerization according to step pre-a2)is carried out continuously.

In a preferred embodiment the preparation of the butyl rubber cementaccording to steps pre-a1) to pre-a3) is carried out continuously.

In step b) according to the invention the butyl rubber or the butylrubbers contained in the butyl rubber cement provided in step a) arebrominated with elemental bromine in the presence of an added aqueousoxidizing agent. Bromine (Br₂) reacts with the butyl rubber polymer toform brominated butyl rubber and hydrogen bromide which is then by theadded aqueous oxidizing agent reoxidized to elemental bromine which canfurther brominate the butyl rubber again forming hydrogen bromide. Thisbromination-reoxidation cycle ideally is repeated until all of theavailable bromine is incorporated into the polymer. Processes known inthe art, however, only allow to utilize sources of bromine to at maximumof 84% as described above.

The elemental bromine necessary to initiate bromination may be either

-   -   added to the butyl rubber cement either in substance or as        solution of elemental bromine, preferably as solution in the        aliphatic medium, more preferably in substance or    -   either additionally or alternatively formed by reaction of        hydrogen bromide or metal bromides or mixtures of hydrogen        bromide or metal bromides as bromine precursors with the aqueous        oxidizing agent in situ.

Preferred metal bromides are alkaline metal, alkaline earth metal orzinc bromide whereby sodium, potassium and zinc bromide are morepreferred and sodium bromide is even more preferred.

Where bromine employment of aqueous solutions of hydrogen bromide ormetal bromides or mixtures of hydrogen bromide or metal bromides arepreferred.

Even more preferred is the employment of concentrated or even saturatedaqueous solutions of metal bromides and the azeotropic mixture ofhydrogen bromide and water comprising 48 wt-% of hydrogen bromide.

In a preferred embodiment elemental bromine and an aqueous oxidizingagent are added to the butyl rubber cement.

The aqueous oxidizing agent may be added to the butyl rubber cementprior to, concurrently with or subsequent to the addition of elementalbromine or the bromine precursors.

In a preferred embodiment the aqueous oxidizing agent is added prior toelemental bromine or the bromine precursors, preferably bromine to allowits dispersal throughout the reaction medium. The aqueous oxidizingagents which have been found suitable for the purposes of the presentinvention are solutions of water soluble peroxides in water which arecapable to oxidize hydrogen bromide or bromide ions to elementalbromine. Preferred water soluble peroxides are exemplified by thefollowing substances: hydrogen peroxide and hydrogen peroxide-formingcompounds, such as per-acids, alkali metal peroxides and adducts ofhydrogen peroxide and alkali metal salts such as sodium percarbonate,whereby aqueous solutions of hydrogen peroxide are even more preferred.

Preferred aqueous solutions of hydrogen peroxide are those comprising 25to 60 wt.-%, preferably 28 to 38 wt.-%, more preferably 32 to 37 wt.-%,even more preferably 34 to 36 wt.-% of hydrogen peroxide.

It was found that the lower the water content in the cement is, thebetter the bromine utilization and oxidation performance with hydrogenperoxide is.

The weight ratio of water soluble peroxides, in particular hydrogenperoxide, to water within the reaction mixture formed by adding theaqueous oxidation agent to the butyl rubber cement is initiallytherefore preferably higher than 0.05, more preferably higher than 0.12,more preferably higher than 0.14. It is clear that the weight ratio ofwater soluble peroxides, in particular hydrogen peroxide, to waterwithin the reaction mixture decreases with proceeding consumption of theoxidizing agent.

In another embodiment the quantity of bromine atoms employed in form ofelemental bromine or bromine precursor or bromine and bromine precursor,preferably only elemental bromine is 0.2 to 1.2 times the molar quantityof double bonds contained in the butyl rubber, preferably 0.3 to 1.0,more preferably 0.6 to 1.0 times the molar quantity.

The aqueous oxidizing agents may either be used in combination withsurfactants or not. In a preferred embodiment no surfactants are added.

Suitable surfactants, if employed, are for example C₆-C₂₄-alkyl- orC₆-C₁₄-aryl-sulfonic acid salts, fatty alcohols and ethoxylated fattyalcohols and the like.

The amount of oxidizing agent used in accordance with the inventiondepends on the amount and kind of bromine source used.

For example from 0.6 to about 5 mol of aqueous oxidizing agentcalculated on hydrogen peroxide per mol of elemental bromine may beused, preferably from 0.8 to 3 mol and more preferably from 0.8 to 1.2mol and even more preferably from 1.0 to 1.2 mol.

If hydrogen bromide or metal bromides as bromine precursors are usedfrom 1 to about 5 mol of aqueous oxidizing agent calculated on hydrogenperoxide per mol of bromide contained in the bromine precursors may beused, preferably from 1.5 to 3 mol and more preferably from 1.5 to 2.4mol and even more preferably from 1.8 to 2.1 mol.

The bromination process may be operated at a temperature of from 0° C.to 90° C., preferably from 20° C. to 80° C. and even more preferably 40to 70° C. and the reaction time may for example be from 1 minute to 24hours, preferably 1 minute to 1 hour, more preferably from 10 to 30minutes. The pressure in the bromination reactor may be from 0.08 to 1mPa.

Agitation of course supports to mix the reactants. In one embodiment themechanical power input is 0.5 W/1 of reaction medium (i.e the butylrubber cement, the added aqueous oxidizing agent and the bromine or thebromine precursor) or above, preferably 0.7 W/1 or above.

Agitation is preferably effected by stirrers and mixers known to thoseskilled in art.

The mechanical power input of stirrers and mixers can for example bedetermined by measuring the electrical power consumption at a certainrotational speed once in the reaction medium and once in air and takingthe difference.

In a preferred embodiment the bromination according to step b) iscarried out continuously for example using a commonly known flow-throughhalogenation reactor.

In a further preferred embodiment the process according to step b) andc) is carried out continuously.

In a further preferred embodiment the process according to steps b), c)and d) is carried out continuously.

The amount of bromination during this procedure may be easily controlledso that the final polymer has the preferred amounts of bromine describedhereinabove.

In step c) the pH-value of the aqueous phase within the heterophasicmixture obtained according to step b) is adjusted to 6 to 13, preferably8 to 12, more preferably 8 to 11 and even more preferably 9 to 10 usinga base.

Throughout this application the term pH-value denotes a pH-valuemeasured at 25° C.

The heterophasic mixture at least comprising a cement comprisingaliphatic medium and brominated butyl rubber and an aqueous phaseobtained in step b) is typically acidic due to formation of hydrogenbromide during the bromination process. The adjustment of the pH-valueneutralizes residual hydrogen bromide, bromine and hydrogen peroxide andas was found here, prevents in particular for pH-values of 8 to 12,preferably 8 to 11 and even more preferably 9 to 10 thepost-halogenation degradation of the brominated butyl rubber, whichnegatively impacts colour, mooney viscosity and molecular weight.

The adjustment is typically made with bases such as aqueous solutions orslurries of alkaline or earth alkaline metal hydroxides or carbonates,preferably with aqueous solutions of alkaline metal hydroxides such assodium and potassium hydroxide, whereby sodium hydroxide is preferred.

If step d3) is applied the cement comprising aliphatic medium andbrominated butyl rubber is washed with an aqueous mixture, preferably anaqueous solution of a base. The pH-value of the aqueous phase may forexample be 8 to 14, preferably 10 to 14, more preferably 12 to 14 andeven more preferably 12 to 13.5.

Throughout this application the term pH-value denotes a pH-valuemeasured at 25° C.

Suitable bases include inorganic and organic bases, whereby inorganicbases like metal carbonates and hydroxides are preferred. Alkaline orearth alkaline metal hydroxides or carbonates are particularlypreferred. Most preferred are aqueous solutions of sodium hydroxide.

In steps d1) or d2) the cement comprising aliphatic medium andbrominated butyl rubber is separated from the aqueous phase. This can bedone in any separation device known to those in the art. In oneembodiment the separation is effected continuously in a separatingapparatus comprising a settling section whereby the separation ispreferably supported by means of a coalescer. Suitable examples ofcoalescers include structured or unstructured packings. Structuredpackings are for example flat plates, flat vanes, roof-shaped vanes andvanes with holes in vertical direction. The vanes or plates may bepositioned rectangular or parallel to the main flow direction or with aslope. Unstructured packings are for example wire mesh, packings made ofrings, spheres, cylinders, irregularly shaped geometries and weirs likedistributor plates that have holes or slits, vertical plates covering aportion of the main flow path. The packings can be made of anytechnically feasible material, e.g. metals, glass, ceramic, coatedmetals, lined metals and polymeric materials like for example PTFE,ETFE, polyethylene (PE), polyetheretherketone (PEEK), Polypropylene(PP), polyamide (PA) and polyvinylidenfluoride (PVDF).

In an optional but preferred step e) volatile components having aboiling point below 250° C. at 1013 hPa are removed from the brominatedbutyl rubber to obtain the brominated butyl rubber in solid form,whereby the residual content of such volatile components is preferablybelow 2000 ppm more preferably below 1000 ppm and even more preferablybelow 500 ppm.

In one embodiment this may be effected by steam stripping orprecipitation for example using a lower alcohol such as isopropanol,followed by drying. In another preferred embodiment of step e) isperformed as disclosed in WO2010/031823 by means of an extruder,preferably a twin screw extruder. Between steps d) and e) a standardwashing step may be applied.

The brominated rubber may cured in a further step. The curing ofbrominated rubbers is well known.

Suitable curing systems for use with the present product are thosealready known in the art for use with brominated butyl rubbers andgenerally include conventional curing systems such as sulphur, resin andperoxide curing systems.

The brominated rubbers and cured brominated rubbers obtainable using theprocess according to the invention may be used as tyre inner liners,treads, sidewalls, adhesives, blends with thermoplastic elastomers,footwear, storage membranes, protective clothing, pharmaceuticalstoppers, linings, and barrier coatings or be used in a process for thepreparation thereof. The brominated rubber cements and brominatedrubbers may further be used to prepare ionomers and polymernanocomposites comprising fillers and ionomers.

The brominated butyl rubbers obtainable according to the inventionwhether in isolated form or as cement obtained in step d) exhibit a veryhigh content of exo-double bonds with bromine in allylic position whichfacilitates cross-linking in commercial applications.

The share of bromine atoms being in allylic position to exo-double bondsas measured by ¹H-NMR typically exceeds 40% or even 50% with respect tothe total bromine content of the brominated butyl rubber as measured byXRF.

Referring to FIG. 1, a solution polymerization reactor 40 is providedwith a feed of monomers M, comprising isoprene and isobutylene, and afeed of the aliphatic medium S via an optional heat exchanger 10,preferably a recuperative heat exchanger, and feed cooler 20. Themonomers may either be pre-mixed with the aliphatic medium or mixedwithin the polymerization reactor 40. The initiator solution, comprisinga carbocationic initiator-activator system of the type used for butylrubber polymerizations is pre-mixed with the aliphatic medium S in ainitiator preparation unit 30 and also introduced to the reactor 40. Thesolution polymerization is then allowed to occur within thepolymerization reactor 40. Solution polymerization reactors 40 of a typesuitable for use in the present integrated process, along with processcontrol and operating parameters of such reactors, are described, forexample, in EP 0 053 585 A, which is herein incorporated by reference.Conversion is allowed to proceed to the desired extent and then areaction stopping agent Q, for example water or an alcohol such asmethanol, is added and mixed into the reactor discharge streamcomprising the aliphatic medium S, un-reacted monomers M and butylrubber IIR in mixer 50. The resulting polymer solution comprisingun-reacted monomers M i.e. isoprene and isobutylene, the aliphaticmedium S and butyl rubber IIR is passed through a recuperative heatexchanger 10 where it is warmed by the incoming feeds to the reactor,while at the same time helping to cool these feeds before they enter thefinal feeds cooler 20. The warmed polymer solution is then directed to adistillation column 60 for removal of the un-reacted monomers. Once theun-reacted monomers have been separated as recycling stream M_(R), theyexit from the top of the column 60 and the separated butyl rubber cement(S, IIR) exits from the bottom of the column 60 to a solutionbromination reactor 70. Additional aliphatic medium S may be provided tothe bromination reactor 70 in order to provide the desired conditionsfor bromination. A feed of bromine or a bromine precursor B and anoxidizing agent OX is also provided to the bromination reactor 70. Thebromobutyl rubber (BIIR) exits the reactor as brominated rubber cement(S, BIIR) and is then finished using finishing equipment 80, as isconventionally known, preferably an extruder. The aliphatic mediumremoved during the finishing step is sent as recycling stream S_(R) tosolvent recovery 110 prior to introduction to solvent purificationsection 120. Additional aliphatic medium S_(F) may be added beforepurification 120 or afterwards, if the medium has already beenpre-purified. The purified common aliphatic medium is recycled back tothe recuperative heat exchanger 10 final feed cooler 20 for re-use inthe process. The un-reacted monomers separated from the polymer solutionin the distillation column 60 are sent as recycle stream M_(R) tomonomer recovery unit 90 and are then purified in monomer purificationsection 100 prior to being recycled back to the recuperative heatexchanger 10 and feed cooler 20. Additional fresh monomers M_(F) may beadded either prior to monomer purification 100 or afterwards, if themonomers have been pre-purified. The description of the process givenhereinabove is exemplary and can be applied to all common aliphaticmedia compositions as well as to all monomer and product compositionsmentioned herein.

It is within the scope of the present invention that the composition ofthe aliphatic medium may have a slightly varying composition before andafter removal of the un-reacted monomers due to different boiling pointsof its components.

EXAMPLES Example 1 Polymerization and Distillation

A reactor of 4 litre total capacity was run in a continuous mode. Feedsto the reactors were 6.438 kg/h of isobutene, 0.150 kg/h of isoprene and5.382 kg/h of an aliphatic medium comprising

-   -   2.0 wt.-% butanes and pentanes having a boiling point below        45° C. at a pressure of 1013 hPa,    -   97.5 wt.-% pentanes and hexanes having a boiling point in the        range of 45° C. to 80° C. at a pressure of 1013 hPa,    -   0.5 wt.-% hexanes, heptanes and octanes having a boiling point        above 80° C. at a pressure of 1013 hPa,        whereby the aliphatic medium comprises less than 20 wt-% of        cyclic aliphatic compounds resulting in a monomer/aliphatic        medium mass ratio of 55:45.

As initiator, a 1.5 wt.-% 1:1 molar mixture of diethylaluminum chlorideand ethylaluminumdichloride solution in n-hexane activated with 100mol-% of water based on the aluminium content was used in an amount of35 g/h.

The reaction temperature used was −65° C. and a solution having a solidscontent of 14 to 15 wt % was produced. This material had a weightaverage molecular weight of about 420 kg/mol and an isoprene content ofabout 1.8 mol-%. The solution from the reactors was fed to adistillation column with 40 trays and separation of the monomers fromthe rubber solution was performed. The solution was preheated to 42° C.and a re-boiler was used at the bottom of the column to maintain abottom temperature of 113° C. A reflux condenser was used to return partof the overhead stream to the top of the column maintaining atemperature there of 36° C. The separation achieved in the column leftless than 10 ppm of residual isoprene monomer in the separated rubbersolution and 1.2% of aliphatic medium in the overhead monomer stream.The separated monomers were purified, then re-introduced to the solutionpolymerization reactor. The butyl rubber cement thus obtained contained18 wt-% butyl rubber in the aliphatic medium. The water content of thebutyl rubber cement was below 0.1 wt.-%.

Example 2 Halogenation with Elemental Bromine

The butyl rubber cement of Example 1 was halogenated using pilot scalebatch bromination equipment. A 35 wt.-% hydrogen peroxide solution inwater (at a molar ratio of 1.1:1 with bromine to be added) wasintroduced into this solution and the resulting mixture was agitated at45° C. for up to 2 minutes prior to the addition of elemental bromine.The amount of bromine added was 21.0 kg per ton of butyl rubber. After areaction period of up to 20 minutes, sodium hydroxide solution was addedto the reaction mixture to neutralize any residual hydrogen bromide,bromine and hydrogen peroxide and to adjust the pH-value to 9.5. Theresulting brominated butyl rubber cement was rinsed with water in a 1:1mass ratio.

Antioxidants (irganox), stabilizers (paraplex) and calcium stearate weredispersed in the cement before steam injection was used to removeresidual solvent. The resulting polymer was dried using a hot mill untilless than 0.1% mass loss was achieved, and analyzed using proton NMR todetermine the microstructure. The NMR results are tabulated below.Values are given in mol %.

unchanged double bonds derived exo-double bonds with bromine in from 1,4isoprene incorporation allylic position 0.80 0.73

The brominated butyl rubbers obtainable according to the inventionexhibit a high content of exo-double bonds with bromine in allylicposition which facilitates cross-linking in commercial applications.

The bromine incorporation into the polymer as determined by XRF was 18.0kg/ton resulting in a bromine utilization of 85.7%.

Example 3 Halogenation with 48 Wt % HBr in Water

The butyl rubber cement of example 1 was halogenated using pilot scalebatch bromination equipment. A 35 wt.-% hydrogen peroxide solution inwater (at a molar ratio of 2.05:1 with HBr to be added) was introducedinto this solution and the resulting mixture was agitated at 45° C. forup to 2 minutes prior to the addition of 48% wt hydrogen bromide inwater. The amount of hydrogen bromine (48% by weight) added was 49 kgper ton of butyl rubber.

After a reaction period of 3 minutes, sodium hydroxide solution wasadded to the reaction mixture to neutralize any residual hydrogenbromide, bromine and hydrogen peroxide and to adjust the pH-value to9.5. The resulting brominated butyl rubber cement was rinsed with waterin a 1:1 mass ratio.

Antioxidants (irganox), stabilizers (paraplex) and calcium stearate weredispersed in the cement before steam injection was used to removeresidual solvent. The resulting polymer was dried using a hot mill untilless than 0.1% mass loss was achieved, and analyzed using proton NMR todetermine the microstructure. The NMR results are tabulated below.Values are given in mol %.

unchanged double bonds derived exo-double bonds with bromine in from 1,4isoprene incorporation allylic position 0.71 0.74

The bromine incorporation into the polymer as determined by XRF was 18.0kg/ton resulting in a bromine utilization of 76.5%.

Example 4 Continuous Halogenation with Elemental Bromine

The butyl rubber cement of example 1 was halogenated using a continuouspilot scale bromination equipment. The equipment with is used based on ahigh-shear mixer in combination with an agitated 161 vessel (mechanicalpower input in vessel W/1).

A solution of 35 wt.-% hydrogen peroxide in water and bromine (at amolar ratio of 1.1:1 H2O2:bromine) were mixed into 34 kg/h of the rubbersolution at 45° C. using the a high-shear mixer. The amount of bromineadded was in the ratio of 19 kg per ton of base rubber.

After a residence time of 20 minutes, sodium hydroxide solution wasadded to the reaction mixture to neutralize any residual hydrogenbromide, bromine and hydrogen peroxide and to adjust the pH-value to9.5. The brominated butyl rubber cement was rinsed with water in a 1:1mass ratio.

Antioxidants (irganox), stabilizers (paraplex) and calcium stearate weredispersed in the cement before steam injection was used to removeresidual solvent. The resulting polymer was dried using a hot mill untilless than 0.1% mass loss was achieved, and analyzed using proton NMR todetermine the microstructure. The NMR results are tabulated below.Values are given in mol %.

unchanged double bonds derived exo-double bonds with bromine in from 1,4isoprene incorporation allylic position 0.60 0.80

The bromine incorporation into the polymer as determined by XRF was 18.0kg/ton resulting in a bromine utilization of 94.7%.

1. A process for the preparation of cements comprising aliphatic mediumand at least one brominated butyl rubber comprising at least the stepsof: a) providing a butyl rubber cement comprising A) 5 to 30 wt-%,preferably 8 to 25 wt-%, more preferably 10 to 22 wt.-% of at least one,preferably one butyl rubber B) 0 to 5 wt-%, preferably 0 to 0.9 wt-%,more preferably 0 to 0.6 wt.-% and more preferably 0 to 0.4 wt.-% ofwater C) and an amount of an aliphatic medium comprising at least 50wt.-% of one or more aliphatic hydrocarbons having a boiling point inthe range of 45.0° C. to 80.0° C. at a pressure of 1013 hPa, selected insuch a manner that the sum of A), B) and C) adds up to from 96 to 100wt-%, preferably to from 98 to 100 wt.-% and more preferably from 99 to100 wt.-% and even more preferably 100 wt.-% of the total amount ofbutyl rubber cement b) brominating the butyl rubber or the butyl rubberscontained in the butyl rubber cement provided in step a) with elementalbromine in the presence of an added aqueous oxidizing agent in order toobtain a heterophasic mixture at least comprising a cement comprisingaliphatic medium and brominated butyl rubber and an aqueous phase andeither c) adjusting the pH-value of the aqueous phase, preferably withinthe heterophasic mixture obtained according to step b), to 6 to 13,preferably 8 to 12, more preferably 8 to 11 and even more preferably 9to 10 using a base d1) separating the cement comprising aliphatic mediumand brominated butyl rubber from the aqueous phase or d2) separating theheterophasic mixture obtained according to step b) to obtain the cementcomprising aliphatic medium and brominated butyl rubber and an aqueousphase and d3) washing the cement comprising aliphatic medium andbrominated butyl rubber with an aqueous mixture, preferably an aqueoussolution of a base.
 2. The process according to claim 1, wherein thebutyl rubber cement is prepared in process comprising at least the stepsof pre-a1) providing a reaction medium comprising an aliphatic mediumcomprising at least 50 wt.-% of one or more aliphatic hydrocarbonshaving a boiling point in the range of 45° C. to 80° C. at a pressure of1013 hPa, and a monomer mixture comprising at least one C₄ to C₇isoolefin, at least one C₄ to C₁₄ conjugated diene and either no one ormore than one further co-polymerizable monomers. in a mass ratio ofmonomer mixture to aliphatic medium of from 35:65 to 99:1, preferablyfrom 50:50 to 85:15 and even more preferably from 61:39 to 80:20;pre-a2) polymerizing the monomer mixture within the reaction medium toform a butyl rubber solution comprising a butyl rubber which is at leastsubstantially dissolved in the medium comprising the aliphatic mediumand residual monomers of the monomer mixture; pre-a3) separatingresidual monomers of the monomer mixture from the butyl rubber solutionto form the butyl rubber cement, whereby the separation is preferablyperformed by distillation.
 3. The process according to claim 1 or 2,wherein the butyl rubber comprises repeating units derived from 92.0 to99.5, preferably 92.0 to 99.0 and more preferably 97.5 to 98.5 or 94.0to 96.6 mol-% of at least one, preferably one C₄ to C₇ isoolefin;preferably isobutene and 0.5 to 8.0, preferably 1.0 to 8.0 and morepreferably 1.5 to 2.5 or 3.5 to 6.0 mol-% at least one, preferably oneC₄ to C₁₄ conjugated diene, preferably isoprene or wherein the butylrubber comprises repeating units derived from i) at least one,preferably one C₄ to C₇ isoolefin; preferably isobutene ii) 0.5 to 8.0,preferably 1.0 to 8.0 and more preferably 1.5 to 2.5 or 3.5 to 6.0 mol-%at least one, preferably one C₄ to C₁₄ conjugated diene, preferablyisoprene and iii) 0.1 to 20, preferably 1 to 20 wt-% of furtherco-polymerizable monomers whereby the repeating units derived from i),ii) and iii) add up to 100 mol-% of the repeating units contained in thebutyl rubber.
 4. The process according to anyone of claims 1 to 3,wherein the butyl rubber is a copolymer of isobutene and isoprenecomprising 1.5 to 2.5 mol-% repeating units derived from isoprene. 5.The process according to anyone of claims 1 to 4, wherein the aliphaticmedium has a content of cyclic aliphatic hydrocarbons of less than 25wt.-%, preferably less than 20 wt.-%, more preferably of from 0.01 to 20wt.-%, even more preferably of from 5 to 20 wt.-%.
 6. The processaccording to anyone of claims 1 to 5, wherein the aliphatic medium has acontent of cyclohexane of less than 5 wt.-%, preferably less than 2.5wt.-%.
 7. The process according to anyone of claims 1 to 6, wherein theelemental bromine necessary to perform step b) is either added to thebutyl rubber cement either in substance or as solution of elementalbromine in the aliphatic medium, preferably in substance or eitheradditionally or alternatively formed by reaction of hydrogen bromide ormetal bromides or mixtures of hydrogen bromide or metal bromides asbromine precursors with the aqueous oxidizing agent in situ.
 8. Theprocess according to anyone of claims 1 to 7, wherein elemental bromineand an aqueous oxidizing agent are added to the butyl rubber cement instep b).
 9. The process according to anyone of claims 1 to 8, whereinthe aqueous oxidizing agent is added to the butyl rubber cement priorto, concurrently with or subsequent to the addition of elemental bromineor the bromine precursors.
 10. The process according to anyone of claims1 to 9, wherein the aqueous oxidizing agent is an aqueous solution ofhydrogen peroxide comprising 25 to 60 wt.-%, preferably 28 to 38 wt.-%,more preferably 32 to 37 wt.-%, even more preferably 34 to 36 wt.-% ofhydrogen peroxide.
 11. The process according to anyone of claims 1 to10, wherein the weight ratio of water soluble peroxides, in particularhydrogen peroxide, to water within the reaction mixture formed by addingthe aqueous oxidation agent to the butyl rubber cement is initiallyhigher than 0.05, more preferably higher than 0.12, more preferablyhigher than 0.14.
 12. The process according to anyone of claims 1 to 11,wherein the quantity of bromine atoms employed in form of elementalbromine or bromine precursor or bromine and bromine precursor,preferably only elemental bromine in step b) is 0.2 to 1.2 times themolar quantity of double bonds contained in the butyl rubber, preferably0.3 to 1.0, more preferably 0.6 to 1.0 times the molar quantity.
 13. Theprocess according to anyone of claims 1 to 12, wherein no surfactantsare added.
 14. The process according to anyone of claims 1 to 13,wherein 0.6 to 5 mol of aqueous oxidizing agent calculated on hydrogenperoxide per mol of elemental bromine are used, preferably from 0.8 to 3mol and more preferably from 0.8 to 1.2 mol and even more preferablyfrom 1.0 to 1.2 mol or if hydrogen bromide or metal bromides as bromineprecursors are used from 1 to 5 mol of aqueous oxidizing agentcalculated on hydrogen peroxide per mol of bromide contained in thebromine precursors, preferably from 1.5 to 3 mol and more preferablyfrom 1.5 to 2.4 mol and even more preferably from 1.8 to 2.1 mol. 15.The process according to anyone of claims 1 to 14, wherein step b) isoperated at a temperature of from 0° C. to 90° C., preferably from 20°C. to 80° C. and even more preferably 40 to 70° C.
 16. The processaccording to anyone of claims 1 to 15, wherein in step b) the reactiontime is from 1 minute to 1 hour, preferably from 10 to 30 minutes. 17.The process according to anyone of claims 1 to 16, wherein in step b)the mechanical power input is 0.5 W/1, preferably 0.7 W/1 or more toagitate the butyl rubber cement, the added aqueous oxidizing agent andthe bromine or the bromine precursor in step b).
 18. The processaccording to anyone of claims 1 to 16, wherein step b) is carried outcontinuously.
 19. The process according to anyone of claims 1 to 17,wherein the bases employee in step c) or d3) are aqueous solutions orslurries of alkaline or earth alkaline metal hydroxides or carbonates,preferably with aqueous solutions of alkaline metal hydroxides such assodium and potassium hydroxide, whereby sodium hydroxide is preferred.20. The process according to anyone of claims 1 to 19, wherein step d1)or d2) is effected continuously in a separating apparatus comprising asettling section whereby the separation is preferably supported by meansof a coalescer.
 21. The process according to anyone of claims 1 to 20,wherein the process further comprises a step e) wherein volatilecomponents having a boiling point below 250° C. at 1013 hPa are removedfrom the brominated butyl rubber to obtain the brominated butyl rubberin solid form, whereby the residual content of such volatile componentsis preferably below 2000 ppm more preferably below 1000 ppm and evenmore preferably below 500 ppm.
 22. The process according to claim 21,wherein the removal is effected by a process using an extruder,preferably a twin screw extruder
 23. The process according to anyone ofclaims 1 to 22, wherein the brominated butyl rubber is cured in afurther step, preferably using a sulphur, resin and peroxide curingsystems.
 24. The process according to anyone of claims 1 to 23, whereinthe brominated butyl rubber comprises a share of bromine atoms being inallylic position to exo-double bonds as measured by 1H-NMR exceeding40%, preferably 50% with respect to the total bromine content of thebrominated butyl rubber as measured by XRF.
 25. Use of the brominatedrubbers or cured brominated rubbers obtainable according to claims 22 to24 as tyre inner liners, treads, sidewalls, adhesives, blends withthermoplastic elastomers, footwear, storage membranes, protectiveclothing, pharmaceutical stoppers, linings, and barrier coatings or in aprocess for the preparation thereof.